Restore detailed entity information in watchdog dumps

[electronicboy]

Watchdog dumps lost their per-entity detail in 1.21.4. When the server thread is stuck, the dump still prints the thread stack, but not which entity is being ticked or what state it is in — which is often the part that actually identifies the problem. An excessive movement vector, or the position of a busted entity so it can be found and removed, is exactly the information that makes a hang diagnosable, and its absence has been noticed more than once.

The instrumentation was never removed, only the readout. ServerLevel still sets and clears currentlyTickingEntity around every tickNonPassenger, and Entity still records the move() start position and move vector under posLock, so servers have been paying for the tracking since 1.21.4 with no way to read any of it back out.

It was dropped incidentally while the Detail more information in watchdog dumps feature patch was inlined into the per-file patches (48f34f8c90, 13b890950d, 3b0b3a0aef) — the call site was replaced with dumpAllChunkLoadInfo, the bodies were emptied, and the four Entity accessors that exposed the move state went with them, leaving those fields private with no reader.

This restores dumpTickingInfo/dumpEntity and the accessors. Notes on the two judgement calls:

• The readout lives in WatchdogThread rather than FeatureHooks, since none of it is chunk-system dependent.
• The dump is wrapped in a catch-all. It reads concurrently mutating entity state off the server thread, so an exception there would previously have cost both the thread dump and the halt that follows it on a long timeout.

Verified by hanging the server thread inside Entity#move (fall damage is dispatched from within move, so the move-vector branch is exercised too) and reading the early-warning dump:

Ticking entity: minecraft:pig, entity class: net.minecraft.world.entity.animal.pig.Pig
Entity status: removed: false, valid: true, alive: true, is passenger: false
Entity UUID: 7b2d530e-14b9-4265-8c75-0e00c7336f7d
Position: world: 'world' at location (0.5, -60.0, 0.5)
Velocity: (0.0, -2.0258051816346994, 0.0) (in blocks per tick)
Entity AABB: AABB[0.05, -60.0, 0.05] -> [0.95, -59.1, 0.95]
Move call information:
Start position: (0.5, -59.82978164948692, 0.5)
Move vector: (0.0, -2.0258051816346994, 0.0)

Two limits worth knowing: only the outermost ticking entity is reported, since currentlyTickingEntity is a single reference assigned only when null; and the packet-handling branch is compile-verified only, as testing it needs a connected client.

[papermc-pr-publishing]

Last updated for: 5bf65680a1d9009b0681ad462ba62516efc3a0b6.

Download the Paperclip jar for this pull request: paper-14242.zip

Maven Publication

The artifacts published by this PR:

• 📦 io.papermc.paper:dev-bundle:26.2.local-SNAPSHOT
• 📦 io.papermc.paper:paper-api:26.2.local-SNAPSHOT

Repository Declaration

In order to use the artifacts published by the PR, add the following repository to your buildscript:

repositories {
    maven("https://maven-prs.papermc.io/Paper/pr14242") {
        name = "Maven for PR #14242" // https://github.com/PaperMC/Paper/pull/14242
        mavenContent {
            includeModule("io.papermc.paper", "dev-bundle")
            includeModule("io.papermc.paper", "paper-api")
        }
    }
}